Embodiments of the present invention relate generally to devices for charging objects and static control devices, and more particularly to the use of certain materials in charge application and static neutralization processes.
In many manufacturing, processing, and packaging systems, it is desirable to place a charge on an object (often referred to as “pinning” an object) to aid in the proper stacking or alignment of various objects. For example, when stacking catalogs at the end of a conveyer, it is difficult to arrange for each of the catalogs to maintain its position so that the catalogs are positioned in a tight, vertically registered stack. The proper alignment of the catalogs is easier to maintain when a charge is placed on each of the catalogs. The tendency of charged catalogs to “stick” together facilitates transporting a stack of catalogs to another location for strapping and/or shrink-wrapping without catalogs slipping from the stack or becoming otherwise misaligned. Maintaining the catalogs in a properly aligned stack prevents damage to misaligned catalogs during the shrink-wrapping or strapping process.
It can also be useful to place a charge on ribbons that are to be tacked together. When two ribbons are being processed so as to overlay each other, it is common for air to become trapped between the ribbons. By placing a static charge on the ribbons, air that is disposed between the ribbons can be displaced which helps prevent “dog ears” and creases in the tacked ribbons. In a similar fashion, placing a charge on a web can be used to firmly position the web on a roller and to reduce slippage between the web and the roller.
Conventional ionizing devices utilize one or more rows of pins to introduce ions into the surrounding gas (such as air) and form a layer on one side of an object. Such conventional devices have several drawbacks. For example, since the ambient gas (e.g., air) is the medium for transporting the ions, energy stored on the object may be affected by ambient temperature, relative humidity, and turbulence. This may be especially true for less mobile positive ions. Additionally, dust and debris may accumulate in the charging devices, thereby contaminating and reducing the long-term efficiency thereof. Further, the pins suffer from high erosion rates due to electron bombardment. The ions attach themselves to particles in the gas, causing debris to pelt the pins, particularly when no object is in proximity to the pins for charging. The pins may also erode quickly due to corrosive contaminate build-up caused by electric fields that are created around the pins as a result of the ion generation process. Pin erosion can lead to uneven charge application and equipment malfunction. The common solution is to manufacture the pins out of harder materials, but the pin material merely slows rather than prevents erosion.
The pins themselves can also contribute to uneven charge distribution. Sharper pins produce more electrons. Pins may additionally have disparate resistances, ranging up to differences of 20% between adjacent pins. As a result, one pin sees another as a load and an uneven charge distribution develops as less ions move to the gas in the vicinity of the pin disparities.
It is therefore desirable to provide an ionizing device that can apply a charge to an object without being susceptible to environmental variations and can provide a more evenly distributed ion field while still being capable of installation into existing equipment, such as conveyors.
In certain other manufacturing, processing, and packaging systems, it is undesirable to have charge on an object. For example, a variety of processes involve the use of webs that are wound, unwound and/or rewound. Frictional contact between the web and rotating or stationary members and guide devices may cause an accumulation of both positive and negative static charges on the web. Some webs, for example, paper webs, readily accept and hold static charges. Build-up of static charges in the web can impact equipment or process performance and functionality and web charges may cause attraction or repulsion of the web from transport surfaces, interfering with proper transport and direction of the web through the process equipment.
Further, electrostatic charges under such circumstances may present significant hazards to operator safety, product quality, and electronic process control. If the charge level on the roll or web reaches a critical limit, a spark can occur, arcing to nearby conductive objects. Critical electronic components may suffer costly damages, and nearby personnel may be injured.
It is therefore desirable to provide a device that can more effectively dissipate the static charge on a passing object.